1. Field of the Invention
The present invention relates to an automatic transmission, and more particularly to an automatic transmission in which a drum is supported by only one bearing in normal operation, and another bearing is caused to function as a bearing only in response to an abnormal external force.
2. Description of the Related Art
An automatic transmission typically includes a speed change mechanism for shifting between a plurality of speeds by engaging and disengaging a clutch and a brake. Such automatic transmissions are provided with two or more clutches, each clutch including a drum, a piston, a canceller, etc.
In this type of automatic transmission, bearing(s) rotatably support the clutch drum at one point or at both ends, i.e. at two points. When support is provided at only one point, the axial length of the bearing must be considerably increased to ensure that the drum will not tilt excessively upon application of an external force. On the other hand, when support is provided at two points, the two bearings must each have a sufficient axial length to ensure sufficient durability.
Therefore, in a conventional automatic transmission, a bearing having a large axial dimension is disposed at the end of a passage for supplying pressure oil, irrespective of whether support is provided at one point or two, thus requiring lengthening of the axial dimension of the drum, making it difficult to reduce the weight and size of the drum, and, by extension, making it difficult to reduce the size and weight of the automatic transmission.